Shell scripts are a powerful way to automate tasks on the command line. To make these scripts more interactive and versatile, it’s often necessary to prompt the user for input. In this tutorial, we’ll explore different methods of taking user input in shell scripts.
1. Using read Command
The most common method to obtain user input in shell scripts is by using the read command. The read command allows you to prompt the user for input and store their response into a variable.
Example:
1#!/bin/bash
2
3echo "Please enter your name:"
4read name
5
6echo "Hello, $name! Nice to meet you."
Output:
bash script.sh
Please enter your name:
Anita
Hello, Anita! Nice to meet you.
In this script, the read command is used to store the user’s input into the $name variable. The input can be any text entered by the user.
To ensure that users provide valid or expected inputs, we can combine the read command with conditional statements. For example:
1#!/bin/bash
2
3read -p "Enter your age: " age
4
5if [[ $age =~ ^[0-9]+$ ]]; then
6 echo "Your age is valid."
7else
8 echo "Invalid age provided. Age should be numeric only."
9fi
In this script snippet, the read command is used to capture the user’s input into the $age variable. The subsequent if-statement checks whether the input consists only of digits using regular expressions.
Output:
bash script.sh
Enter your age: 22
Your age is valid.
bash script.sh
Enter your age: twenty
Invalid age provided. Age should be numeric only.
2. User Input from Command Line Arguments
Another way to get user input is using command line arguments which are passed to the script being executed. Bash scripts can access command line arguments through special variables: $1, $2, $3, and so on. We will learn about them in the later lesson but they are just positional arguments passed into the script.
$0 represents the script filename itself, while $1 and $2 hold the first and second command line arguments passed when running the script. We can also pass more than 2 arguments, but this example demonstrates only two command line arguments.
1#!/bin/bash
2
3echo "Script name: $0"
4echo "First argument: $1"
5echo "Second argument: $2"
Output:
bash my_script.sh Robert 23
Script name: my_script.sh
First argument: Robert
Second argument: 23
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